In the field of photomechanical process technology, photographic materials with excellent original-producibility, stable processing solutions and simplified replenishment systems are required to deal with diversified and complicated print forms.
Originals to be employed in a line work process are often composed of phototypeset letters, hand-written letters, illustrations and halftone dot image photographs. Accordingly, the originals often combine several images having a different concentration and a different line width. Photomechanical cameras and photographic materials capable of finishing the images from such originals with good reproducibility, as well as image-forming methods applicable to such photographic materials, are needed in this field. On the other hand, in photomechanical processes for producing catalogs or large-sized posters, a blow-up or reduction of the dot image photographs is often performed. In the photomechanical processes using enlarged dot images, the dots are coarsened to give blurred photoprints. On the other hand, in the photomechanical processes for forming reduced photoprints, fine dots with an enlarged ratio of lines/inch are to be photographed. Accordingly, an image-forming method with a much broader latitude is desired to maintain the reproducibility of halftone dot images in these photomechanical processes.
As the light source for a photomechanical camera, a halogen lamp or xenon lamp is employed. In order to obtain a sufficient photographing sensitivity to the light source, the photographic material employed in the photomechanical process is generally ortho-sensitized. However, it was found that the ortho-sensitized photographic materials are much more influenced by the chromatic aberration of the lens and therefore the quality of the images formed is frequently reduced because of that influence. It was further found that the deterioration of the image quality is more noticeable where a xenon lamp is used as the light source.
As a system for satisfying the demand for the broad latitude, a method is known in which a lith-type silver halide photographic material composed of silver chlorobromide (having a silver chloride content of at least 50% or more) is processed with a hydroquinone-containing developer in which the effective concentration of the sulfite ion therein is extremely low (generally, to 0.1 mol/liter or less) to obtain a line image or halftone dot image having a high contrast and a high blackened density in which the image portions and the non-image portions are clearly differentiated from each other. However, the method has various drawbacks. Specifically, since the sulfite concentration in the developer to be employed in the method is low, development is extremely unstable to aerial oxidation. To stabilize the activity of the processing solution, various means must be used. As a result, the processing speed is extremely slow, and the working efficiency is poor.
Accordingly, an improved image-forming system is desired, which is free from the instability of image formation during the above-mentioned development method (lith-development system) and which may be processed with a processing solution having an excellent storage stability to give photographic images having ultra-hard photographic characteristics. As one example, a system of forming an ultra-hard negative image having a gamma value of more than 10 has been proposed, for example, in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606 and 4,311,781. In that system, a surface latent image-type silver halide photographic material containing a particular acylhydrazine compound is processed with a developer which has an excellent storage stability and which contains a sulfite preservative in an amount of 0.15 mol/liter or more, at a pH value of from 11.0 to 12.3. The image-forming system is characterized by the fact that a silver iodobromide- or silver chloroiodobromide-containing photographic material can be processed, while only a high silver chloride content-having silver chlorobromide photographic material can be processed by the conventional ultra-hard image-forming method.
The image-forming system is excellent in that an image with a sharp halftone dot image quality is formed, the process proceeds stably at a high speed, and the reproducibility of the original is good. However, a further improved system with a further elevated original reproducibility is still desired for the purpose of satisfactorily dealing with diversified print forms.
Additionally, it is desirable to perform plate making work and dot to dot work in a light environment to improve working efficiency. Therefore, development of photographic materials for photomechanical process which can be handled under a condition that can be called substantially a daylight room as well as development of an exposure printer usable for the materials has been undertaken.
Photographic materials for daylight use, as referred to herein, mean those which can be safely used for a long period of time under a safelight having a wavelength of substantially 400 nm or more without ultraviolet components.
The daylight photographic materials used in the plate making work and the dot to dot work are those which are utilized for negative image/positive image conversion or positive image/positive image conversion in which an original of a developed film having letter or halftone dot images thereon is contacted with a dot-to-dot working photographic material for contact exposure. The materials must satisfy the following two requirements:
(1) in the negative image/positive image conversion with the materials, the halftone dot images as well as line images and letter images can be converted in accordance with the dot area, line width and letter image width; and
(2) tone regulation of the halftone dot images as well as regulation of the line width of the letter and line images is possible.
Accordingly, various photographic materials for daylight dot to dot work which may satisfy these requirements have heretofore been proposed.
However, in high technological image-conversion work, for example, in the formation of super-imposed letter images by contact dot-to-dot work, the conventional method of conducting the daylight dot-to-dot work step by using a daylight photographic material is inferior to the dark dot-to-dot work method of using conventional dark dot-to-dot work photographic material. Specifically, the quality of the super-imposed letter images formed by the former is worse than that of the images formed by the latter.
The method of forming super-imposed letter images by contact dot-to-dot work will be explained in more detail hereunder with reference to the sole Figure of this specification. As shown in the Figure, transparent or semitransparent supports (a) and (c) (generally, polyethylene terephthalate film having a thickness of approximately 100 .mu.m is used) are attached to a letter or line image-containing film (line original) (b) and a halftone dot image-containing film (halftone original) (d), respectively, to form a combined original, and a dot-to-dot working photographic material (e) is brought into contact with the halftone original (d) so that the emulsion surface of the material (e) faces and contacts the halftone image surface of the original (d). Then the material is exposed to light through the combined original by contact exposure.
After exposure, the material is developed to form transparent line image portions in the dot images.
The important point in this method of forming super-imposed letter images is that the negative image/positive image conversion is ideally effected in accordance with the dot area and the line width of the halftone original and the line original, respectively. However, as is obvious in the Figure, the line original is exposed to the dot-to-dot working photographic material (e) via the support (c) and the halftone original (d), while the halftone original (d) is directly exposed to the emulsion surface of the material (e) by contact exposure therewith.
Accordingly, if an exposure amount sufficient for faithful negative/positive conversion of the halftone original is imparted to the material, it would be an out-of-focus exposure to the line original because of the spacers of the support (c) and the halftone original (d) so that the line width in the transparent line image portions in the dot images formed would be narrow. This is the reason for the reduction in the quality of the transparent line image portions in the dot images formed.
In order to overcome the above-mentioned problems, a system of using hydrazine has been proposed, for example, in JP-A-62-80640, JP-A-62-235938, JP-A-62-235939, JP-A-63-104046, JP-A-63-103235, JP-A-63-296031, JP-A-63-314541 and JP-A-64-13545. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) However, the system is not sufficient and further improvement of the system is desired.
As a means of improving the original-reproducibility and improving the quality of the super-imposed letter image formed, for example, a method of silver-imagewise releasing a development inhibitor from a carbonyl group-containing redox compound is known, as illustrated in JP-A-61-213847 or JP-A-64-72139. However, the method is still unsatisfactory because it fails to achieve both sharp dot image quality (which is one characteristic merit of the system of using a hydrazine derivative) and sufficient processing stability (such stability measuring that the fluctuation of the quality of the image formed is negligible with respect to the variation of the pH value, the sodium sulfite content and the developer composition in the processing system).
Accordingly, it is desired to develop a means for producing with a stable developer photographic images which are hardly influenced by the fluctuation of the composition of the processing solution used and which have a sharp halftone dot image quality, an excellent original-reproducibility and an excellent super-imposed letter image quality.